Present day manufacturing for semiconductor electronics, solar cells, and other technology relies on ion implanter systems for doping or otherwise modifying silicon and other types of substrates. A typical ion implanter system performs the doping by generating an ion beam and steering it into a substrate so that the ions come to rest beneath the surface. In many applications, ion beams having a defined shape and ion beam area such as a spot beam or ribbon beam are scanned over a substrate to implant a species into a substrate area that is larger than the ion beam area. Alternatively, a substrate may be scanned with respect to a stationary beam or both substrate and beam may be scanned with respect to one another. In any of these circumstances many applications require that a substrate be implanted uniformly over a large portion of the substrate.
One type of non-uniformity that may be produced by an ion beam is termed “micrononuniformity” and refers to the presence of regular patterns of varying ion dose on a substrate. Such patterns may appear, for example as stripes of varying ion dose that are observed when a substrate is scanned along a particular direction. For example, if an ion beam exhibits a periodic variation in beam current while a substrate is scanned, a pattern of micrononuniformity made up of high ion dose regions alternating with low ion dose regions may result. Such a periodic variation in beam current may be generated from different sources within the ion implanter. For example, mechanical sources such as vibrations within a beam processing component such as a lens may induce fluctuation (modulation) in beam current. Notably, fluctuations within a beamline component such as an electrostatic component, a magnetic component, or a mechanical component may cause changes in ion beam intensity at the substrate. In some cases, the beam position, beam size, and/or beam divergence and direction may fluctuate as the ion beam propagates through the beamline.
Moreover, the frequency associated with the periodic variation in beam current is often relatively low with respect to a frequency required to “average out” the beam current variation for a given scan speed of a substrate. For commonly used scan speeds of a substrate along a given direction, the cross-sectional dimension of the ion beam is often too small to average out such beam current variation, thereby resulting in a striped pattern of micrononuniformity being produced upon a substrate during scanning.
Other non-uniformity may result from high frequency variation in ion beam properties that are also associated with sharp changes in ion current density within an ion beam, such as “hot spots.” Typically such non-uniformities may not be detected until after substrates have been processed. Moreover, depending upon the requirements of a given application, ion dose non-uniformity as little as a few tenths of one percent or even less may be unacceptable. An undetected micrononuniformity may therefore result in the inadvertent production of unusable product. It is with respect to these and other considerations that the present improvements have been needed.